1. Field of the Invention:
This invention relates generally to an automatic focusing apparatus, and more particularly, to an economical and simple automatic sonar controlled focusing apparatus wherein lens movement and sonar ranging occur in proportionately related elapsed time intervals.
2. Description of the Prior Art:
Ultrasonic ranging systems are well known for cameras and in each of the systems, ultrasonic energy is transmitted toward a subject to be photographed, and the subject reflects the ultrasonic energy back to the camera. Characteristics of the transmitted and received signals may be compared to derive a control signal representative of subject distance. The control signal can be thereafter used to drive the lens mount of the camera to a position corresponding to the subject distance whereby the subject will be in focus.
U.S. patent application Ser. No. 840,802 entitled "Ultrasonic Ranging System for a Camera" by J. Muggli filed in common assignment herewith provides an ultrasonic ranging system for a camera having a lens mount movable to a position at which a subject being photographed is in focus. The system includes an ultrasonic transducer that responds to a keying pulse by transmitting a relatively short burst of frequency modulated ultrasonic energy and a synchronized receiver for processing an echo signal produced by the transducer upon receipt of an echo upon a predetermined time interval. The receiver produces a range signal with a characteristic related to the distance of a subject being photographed from the camera. The range signal representing the subject distance may thereafter be used in a manner as is more fully disclosed in U.S. patent application Ser. No. 729,289 to control a gated pulse generator in a nonlinear manner such that the latter produces a train of pulses whose number is representative of the actual position of the lens mount at which the subject will be in focus, and includes a focusing mechanism having means, responsive to the pulse produced by the pulse generator means for displacing the lens mount to the proper position. Such systems are complex and expensive since the range signal must be utilized to control a gated pulse in a nonlinear manner to produce a train of pulses whose number is representative of the actual position of a lens mount. The focusing mechanism must then embody a servo-mechanism to respond to the pulses produced by the pulse generator in order to mechanically displace the lens mount to the proper axial position thereby further contributing to the complex nature of such auto focus arrangements.
Therefore, it is a primary object of this invention to provide a simplified and economical automatic sonar controlled focusing apparatus wherein the lens movement occurs in an elapsed time interval which is directly proportional to the elapsed time interval between which the sonar ranging signal is transmitted and thereafter received subsequent to being reflected by the photographic subject.
It is a further object of this invention to provide a simple and automatic sonar ranging apparatus wherein the lens movement is initiated with the transmission of the sonar ranging signal and wherein the lens movement is thereafter terminated in response to the receipt of the echo from the sonar ranging signal.
Other objects of the invention will be in part obvious and will in part appear hereinafter. The invention accordingly comprises a mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.